1. Field of the Invention
The present invention is broadly concerned with providing a non-invasive technique for the early detection of cancer and other abnormal tissue and, more particularly, to the field of imaging elastic scattering spectroscopy (IESS).
2. Description of the Background
Detecting abnormal tissue early is critical to the successful treatment of disease. Life expectancy of patients with malignancy or cancer, for example, can increase dramatically when abnormal tissue is identified while still in a pre-malignant state. Such tissue regions, dysplasia and carcinoma in situ being typical examples, are ordinarily detected by surgical biopsy. The removed tissue is sent to a pathologist, where it is examined under a microscope for the characteristic morphological changes that indicate abnormal cell growth. Upon receiving the pathology report, the physician can then decide whether further removal of the tissue is indicated.
This method of treatment has a number of serious drawbacks. For example, only a limited number of regions can be biopsied, with the choice of region determined only by its gross appearance in the eyes of the physician. It is therefore quite likely that a problem area, particularly one in an early stage of abnormality, may be missed completely. Another serious drawback of this method of treatment is that since the identification of abnormality must await the pathology report, surgical removal of the abnormal tissue often must be performed during a separate procedure (and sometimes even by successive iterations), thereby increasing risk to the patient, and inconvenience and cost for both the patient and the physician.
Within the last decade or so, a number of all-optical techniques for identifying abnormal tissue have been developed in an attempt to avoid these problems. These approaches have the potential for allowing problem sites to be detected over a large area sensitively and quickly, without having to rely on the subjective judgment of the physician. In addition, because suspicious areas can be identified during the initial examination, diseased tissue can be removed immediately, and completeness of the excision assessed by prompt reimaging of the area in question.
The most developed of these optical techniques makes use of differences in the spectra of fluorescence exhibited by normal and abnormal tissue. This fluorescence is ordinarily excited by laser illumination, and can be either intrinsic or extrinsic. Although numerous groups are working on the development of fluorescence-based systems for cancer diagnosis, to date only one device has reached the commercial market. The LIFE scope, manufactured by Xillix Inc. and marketed by Olympus, Inc., uses ultraviolet laser light to excite tissue autofluorescence through a bronchoscope. It is presently being used by approximately 50 groups worldwide with a cost of upwards of $200,000 per unit. Although this device provides much greater sensitivity than standard white-light bronchoscopy, single procedures can be very time consuming. Even experienced surgeons often require 45 minutes to perform one examination which would take only 3 minutes using standard bronchoscopy equipment. The use of the LIFE scope is not only quite draining for the patient and physician, but also limits greatly the number of patients that can be seen, thereby substantially increasing procedure cost.
Other groups have used Raman signals to identify abnormal tissue, however these signals are extremely weak, and it may be difficult to implement as a practical clinical tool.
A third approach, elastic scattering spectroscopy (ESS), illuminates the sample, and looks at the spectral content of the light scattered from tissue right beneath the surface by using a point probe in contact with the tissue surface. This method has the capability of detecting disorganized epithelial orientation and architecture, morphological changes in epithelial surface texture and thickness, cell crowding, enlargement and hyperchromicity of cell nuclei, increased concentration of metabolic organelles, and the presence of abnormal protein packages. ESS has been used to study the skin, the eyes, the bladder, the prostate and many different regions of the gastrointestinal tract. In one study, ESS was used to differentiate neoplastic from non-neoplastic tissue and adenomatous polyps from hyperplasic polyps in the colon with a predictive accuracy of ˜85%. In another study ESS was used to detect bladder cancer with a sensitivity of 100% and a specificity of 97%. Preliminary tests of this technique in the lower GI tract demonstrated the ability of differentiating between dysplasia, adenoma/adenocarcinoma, and normal mucosa with a sensitivity of 100% and a specificity of 98%. Studies in the skin have demonstrated a sensitivity of 90.3% and a specificity of 77.4% for distinguishing primary melanomas from benign nevi. Over a decade of clinical trials with this instrument in a variety of organ systems has shown that these spectra can provide a sensitivity means of detecting even early abnormal tissue. At present, however, this method is capable of providing single point measurements only, thereby making it inappropriate for routine clinical use.
Therefore, there is a need in the art for a system for detecting ESS signals in a full imaging mode which can be equally applicable to imaging endoscopically and imaging externally for routine clinical use.